1. Field of the Invention
The present invention relates to a pressure-sensitive adhesive composition having antistatic property, and pressure-sensitive adhesive sheets and a surface protecting film obtained by formulating into a form of a sheet or a tape using the composition.
2. Description of the Related Art
Pressure-sensitive sheets comprising an antistatic pressure-sensitive adhesive composition of the present invention is suitably used in plastic products on which static electricity is easily generated. Above all, particularly, the pressure-sensitive adhesive sheet is useful as antistatic pressure-sensitive adhesive sheet and surface protecting film used for avoiding static electricity in an electronic instrument and the like.
A surface protecting film is generally stuck to subject to be protected with pressure-sensitive adhesive applied on the side of the protecting film, and used for the purpose of preventing scratches or staining caused during processing and conveyance of the subject to be protected. For example, a liquid crystal display panel is formed by sticking optical members such as a polarizing plate and a wavelength plate to a liquid crystal cell with pressure-sensitive adhesive. The protecting film is stuck to these optical members stuck to the liquid crystal cell with pressure-sensitive adhesive for the purpose of preventing scratches, staining and the like.
Then, the protecting film is removed by peeling off at the stage when the protecting film becomes unnecessary, for example, this optical member is stuck to the liquid crystal cell. Generally, the protecting film and the optical member are composed of plastic materials, so that electrical insulating property is high and static electricity is caused during friction and peeling off. Accordingly, also when the protecting film is peeled off from the subject to be protected, static electricity is caused to result in deterioration of workability and damage of the subject to be protected. Thus, in order to prevent such defects, various antistatic treatments are applied to the surface protecting film.
For example, a method of preventing electrification by adding one kind or more of a surfactant to pressure-sensitive adhesive to transfer the surfactant from the pressure-sensitive adhesive to an adherend is disclosed (for example, refer to Patent Literature 1). However, with regard to this invention, the surfactant bleeds on the surface of the pressure-sensitive adhesive so easily that staining on the adherend is concerned in the case of applying to the protecting film.
Also, a method of adding an antistatic agent comprising polyether polyol and an alkali metal salt to acrylic pressure-sensitive adhesive to restrain the antistatic agent from bleeding on the surface of the pressure-sensitive adhesive is disclosed (for example, refer to Patent Literature 2). However, bleeding of the antistatic agent can not be avoided also in this method; consequently, in the case of actually applying to the surface protecting film, it has proved that treatment with time and under high temperature causes staining on the adherend due to the bleeding phenomenon.
On the other hand, pressure-sensitive adhesive using no organic solvent has been demanded in recent years from the viewpoint of environmental measures, resources saving and safety.    Patent Literature 1: Japanese Unexamined Patent Publication No. 9-165460    Patent Literature 2: Japanese Unexamined Patent Publication No. 6-128539